1. Field of the invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for adjusting a transmit power of a sounding reference signal in a wireless communication system.
2. Related Art
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (May 2009) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, a physical channel of the LTE can be classified into a downlink channel, i.e., a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH), and an uplink channel, i.e., a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH).
The PUCCH is an uplink control channel used for transmission of an uplink control signal such as a hybrid automatic repeat request (HARQ) positive-acknowledgement (ACK)/negative-acknowledgement (NACK) signal, a channel quality indicator (CQI), and a scheduling request (SR).
An uplink reference signal can be classified into a demodulation reference signal (DMRS) and a sounding reference signal (SRS). The DMRS is a reference signal used in channel estimation for demodulation of a received signal. The SRS is a reference signal transmitted for uplink scheduling by a user equipment to a base station. The base station estimates an uplink channel by using the received SRS, and the estimated uplink channel is used in uplink scheduling.
Meanwhile, 3GPP LTE-advanced (A) which is an evolution of 3GPP LTE is under development. Examples of techniques employed in the 3GPP LTE-A include carrier aggregation and multiple input multiple output (MIMO) supporting four or more antenna ports.
The carrier aggregation uses a plurality of component carriers. The component carrier is defined with a center frequency and a bandwidth. One uplink component carrier and one downlink component carrier are mapped to one cell. When the user equipment receives a service by using a plurality of downlink component carriers, it can be said that the user equipment receives the service from a plurality of serving cells.
There are a plurality of serving cells, and thus a plurality of sounding reference signals can be transmitted in the plurality of serving cells. Since a maximum transmit power of the user equipment is limited, there is a need for a method of adjusting a transmit power of the plurality of sounding reference signals.